Recharge Continued from Page 7
Asked about challenges to recharge, Cameron said those include providing theneeded infrastructureandconsidering soil differences and themovement of salts, pesticides and herbicides. “Management criteria have to be in place,” Cameron said. He and others also said challenges in- clude the difficulty of getting into flooded fields for treatments such as spraying. Cameron saidhe laser-leveled fields for even distribution of water. McKean said his almond trees are on high berms to control water flow, and he usesbothdripand flood irrigation. “It’snot real simple,” he said. McKean said he has concerns about plant health, and said he would like to see more research on rootstocks that might be best suited to recharge condi- tions. He said he would also like to see more research on leaching. King said timing is important inmanag- ing recharge. When water is available, he said, “you have to be prepared to take it.” King said he favors recharge because “it’s replicating natural systems.” McKean said he would like to see “credits” given to growers who use on- farm recharge. (Denni s Pol lock i s a repor t er in F r e s no . He ma y b e c on t a c t e d a t apcompollock@yahoo.com.)
In California, pecans are grown in 17 counties. The leaders inpecanproduction areTulareandColusacounties,withnearly half the acreage. One of the research plots had continu- ous flooding to maintain standing water. In another, there was alternate flooding between two sub-blocks, and in another there was regular irrigation followed by a second irrigation. A control plot had reg- ular flood irrigation. Poly pipe was stretched across about 850 feet of one field. It was fitted with ad- justablegates forwater flow. Terracingwas used to improvewater depth uniformity. Flooding did bring oxygen decreases in theroot zone, but recovery fromthatbegan immediately whenwater was off the field, Bachand said. Management techniques were to allow soils to dry briefly for five or sixdaysor toapply rechargewater toevery other row, then switch rows. The cost of recharge ranged from$35 to $200 an acre, about 1.5% to 9% of the cost of regular operations. BothBachandandDahlkesaidresearch has shownon-farmrechargecanbebene- ficial in other crops besides nuts. Dahlke saidpulsed floodingof almonds
This orchard is flooded as part of groundwater recharge efforts at a San Joaquin Valley nut farm.
showed no significant effect on yield, and onwell-drainedsoils, largeamountsofwa- ter can be recharged. She said it is a viable option for regionswhere large amounts of excess water are less frequently available. “Flooding can create short-lived anoxic conditions in the root zone,” she said, add- ing that the duration of such conditions needs to be managed. Flooding reduces oxygen levels within the soil, inhibiting root respiration and root growth with po- tentially negative effects on crop yield. She added that winter recharge can produce nitrates in the root zone through mineralization of organic nitrogen and might reduce fertilizer needs during
the growing season. The most nitrate is leached within the first few hours of ap- plication, before conditions for denitri- fication are reached, and denitrification plays a greater role in fine textured soils with continuous flooding. Dahlke cited notable differences in soil drainagebetweensandysoilsandthosethat are a fine sandy loam. There are also varia- tions incrop tolerance towaterlogging. The grower panel discussionwasmod- erated by Mohammad Yaghmour, UC or- chard systems advisor for KernCounty. The panel included Fresno County growers Cameron; Mark McKean with McKean Farms; and Ben King, the state’s largest pecan grower with orchards near Visalia and Colusa. King also grows al- monds.He iswithPacificGoldAgriculture.
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Is all salt bad?
The total salts in soil and water can come from several sources. Salts are often measured by the electrical conductivity (EC). The EC for irrigation water is normally a measure of total salts, but it does not tell us which salts make up the composition. Common units of measure are deciSiemens per meter (dS/m) or millimho per centimeter (mmho/cm), 1 dS/m = 1 mmho/cm. The EC is usually a balance of cations and anions reported as meq/l. Cations (+) Anions (-) Calcium Ca Bicarbonate HCO3 Magnesium Mg Carbonate CO3 Sodium Na The predominate cations and anions are listed above. Potassium may be reported but does not usually contribute to salinity issues. Boron and Nitrates may also be reported, these are important for diagnosing toxici- ties and N requirements. Irrigation water samples should be analyzed to tell us how much individual cations and anions are present. When EC measurements are above 4.0, and sodium levels are high, crops may experience reduced soil water availability for root absorption. Crops grown on saline soils must work harder to take up water. These crops may show symptoms of water stress, even when soils are moist. High levels of sodium in the water or soil can lead to poor soil structure decreasing water infiltration, damaging crops and increasing soil pH which changes nutrient availability. If leaching sodium with clean water isn’t an option, keeping calcium as the dominate salt will help reduce the negative effects of sodium. Remember to keep Ca > Mg + Na. Chloride CI Sulfate SO4 Sources: Valley Tech Ag Lab & UC Almond Production Manual publication 3364.
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8 Ag Alert August 11, 2021
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